"Finally," said not one single die-hard fan of FX's thriller "The Strain," "a bunch of historical background on vampires!"

Too bad. That's what viewers saw in the most recent episode of the hit summer series, with professor-Holocaust survivor Abraham Setrakian providing both the origin story and the justification for the wormy bloodbath that's ahead.

It does help, tremendously, that distinguished British actor David Bradley stars as Setrakian, propelling this story forward as the take-no-prisoners sword-cane-carrying vampire hunter. That guy is awesome, whether he's lopping off the heads of the newly hatched undead or making witty, dry observations about his naive companions.

No apologies necessary, then, for the detour to 1944 Poland. That's where Setrakian first saw The Master in sickening action, preying on men in concentration camps during World War II. The now-grizzled senior citizen seemed to vow, even at the time, to destroy the king of all vamps. And fans of the show already have heard bits and pieces about the importance of his lifelong mission, but it's been rather vague and cryptic.

But the details are starting to flow, in flashback form. And for a terse and single-minded man, Setrakian can be very descriptive when prodded. He'd heard tell as a child of a giant-sized blood-sucking demon, but he thought those were just fairy stories made up by his grandmother. Sleep tight?

He knows now that The Master will bring about "a scourge," and a widespread "corruption of flesh and spirit." And in language that his doubting sidekick, the Centers for Disease Control epidemiologist Dr. Ephraim Goodweather, can understand, he dubs The Master "patient zero."

Setrakian, who does not suffer fools but has been pretty darn patient with Eph, says The Master feeds on the blood of his victims.

"Like a vampire?" says an incredulous Eph, using the term for the first time in the series.

Setrakian, as it turns out, prefers the Romanian translation anyway. The word strigoi will likely come up a lot in future episodes, and it does sound mighty forceful when Setrakian spits it at vamps during the decapitation process.

Not only is The Master a blood drainer, he's also an infectious agent, Setrakian tells Eph, capable of wiping out entire populations via those slimy white worms he embeds in his victims. He's also a regular whiz at misdirection and misinformation, which laid blame on the airline for all those dead(ish) bodies on Regis flight #753.

Eph, whose a-ha moment came in the previous episode, still thinks he can somehow persuade the CDC to quarantine hundreds of New Yorkers while he works on a "cure" for what ails them. By the end of the hour, he'll find out otherwise because, at long last, he's realizing that there's a conspiracy afoot and this situation is much bigger than his idealism.

To get video proof of the contagion's effects, he agrees to go with Setrakian to a plane survivor's house. They're not looking for the survivor alone, a wimpy dude named Ansel, but for all the family members he might've eaten/turned by now. (Setrakian has already put down two of the stricken in episode 4 while Eph stood there, mostly stricken).

Since Setrakian sure could use a hand with the heavy lifting, he arms Eph with a nail gun this time. Its ammo is pure silver, so it will at least cause a flesh wound while the old man plays executioner.

At a suburban house in a place that looks nothing like Brooklyn, Eph and Setrakian find Ansel chained in the dog shed with his nasty neighbor/food source. Eph gets his smartphone footage, and Setrakian stacks two more bodies onto his mercy kill pile before torching the place.

The old cliché, "you only hurt the ones you love," is a central tenant of the series, as it was in the bestselling novels on which the show is based, according to "The Strain" mastermind Guillermo del Toro. That explains why Setrakian is making a beeline to each plane victim's family home. The newly turned vampires will go there first, trotting their worms and thirst with them.

"You may think it's a fortune cookie musing, but the element of love is a driving force and a plot point," del Toro said at a Television Critics Assn. panel last month. "It's how the vampires hone in on their victims."

Love had nothing to do with another scene of carnage in this episode, dubbed "The Runaways." Gabriel Bolivar, one of the four survivors from the Regis jumbo jet from Berlin to JFK, has been slowly changing from goth shock rocker to full-fledged predator. His transformation is now complete, judging from his slaughter of the urologist who misguidedly made a house call and the fixer who tried to clean up the crime.

Familial ties most certainly will play a role, though, when a lawyer named Joan, one of the plane survivors, wants to latch onto the throats of her two kids. She's already sniffing them like they're freshly baked cookies. Nanny may have the best intentions – mom has demon eyes! – but she's opening up a can of, sorry, worms by spiriting them away.

While Bradley's Setrakian has quickly become a fan favorite, so has Kevin Durand's manly exterminator extraordinaire, Vasiliy Fet. And though his appearance in this episode is brief, it's significant.

He's already been ruminating on why so many rats are surfacing all over New York. They're running away from a larger predator, he tells his co-worker. So he decides to take a look for himself, popping under a busy Manhattan intersection only to find a nest of a different variety. He smartly hightails it. The blazing midday sunlight is the only thing that stops the horde of vamps from spilling out onto Chambers Street right behind him. That was close.

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